When using Djangos "makemessages" command to collect strings for i18n it only
considers templates with a file extenions of .txt and .html by default. For
more details see:
https://docs.djangoproject.com/en/dev/topics/i18n/translation/#message-files
Also when Django is refering to default template names (e.g. for error handling
or accounts) it always refers to file names with .html as file extension.
To avoid hassle in the future this commit aligns the file extension used for
templates to Djangos default of .html.
jeffrey forman
Daniel Roschka